1. Field of the Invention
The present invention relates to an optical disk apparatus. More specifically, the present invention relates to an optical disk apparatus including a mechanism for moving an optical head.
2. Description of the Related Art
A recording and reproduction apparatus (optical disk apparatus) for recording data to and reproducing data from a disk (recording medium) using an optical head requires a mechanism for moving an optical head from an inner circumference to an outer circumference of a recording region of the disk. A mechanism in which an optical head is moved along a pair of parallel guide members is widely used.
Japanese Patent No. 2902876 discloses a conventional technique adopting such a mechanism in the technique disclosed in Japanese Patent No. 2902876, a driving force for moving an optical head is transferred from a pinion to a rack which are mounted on the optical head. The optical head is slid along a column-shaped guide shaft (guide member). The rack is provided in the optical head in such a manner as to be rotated about the guide shaft.
FIG. 15A is a side view showing a moving mechanism of an optical head described in Japanese Patent No. 2902876.
FIG. 15B is a plan view of the moving mechanism of the optical head of FIG. 15A, viewed in a direction indicated by an arrow B.
The moving mechanism of the optical head described in Japanese Patent No. 2902876 will be described below with reference to FIG. 15A. An optical head 102 is moved along guide shafts 101R and 101L in and out with respect to the plane of the figure.
A rack 103 is pressed by a pressing spring 106 in a direction from the optical head 102 to a small gear 105S. The rack 103 is supported by the guide shaft 101R as a supporting shaft in such a manner as to be freely rotated in a direction indicated by an arrow 201.
Referring to FIGS. 15A and 15B, the optical head 102 is guided by the guide shafts 101R and 101L which are arranged in parallel. The optical head 102 is configured to be moved in a direction indicated by an arrow 202. The rack 103 seizes a shaft bearing 1001 of the guide shaft 101R of the optical head 102 by holding the opposite ends of the shaft bearing 1001, and is supported by the guide shaft 101R in such a manner as to be freely rotated.
A driving force for the optical head 102 is transferred from a driving gear 104 driven by a motor to a large gear 105L. The large gear 105L and the small gear 105S (pinion) are integrated to constitute a stepped gear 105 so that the driving force is decelerated and transferred from the small gear 105S to the rack 103.
As the driving force of the motor causes the rack 103 to be moved in the direction indicated by the arrow 202 (FIG. 15B), the optical head 102 whose shaft bearing 1001 is seized by the rack 103 is moved.
FIG. 16 shows states of the rack 103 and the small gear 105S which are engaged with each other. When the rack 103 and the small gear 105S are too close to each other, the gear teeth of the rack 103 and the small gear 105S interfere with each other, obstructing the transference of a driving force. To avoid such an adverse situation, a certain amount of backlash is provided between the gear teeth of the rack 103 and the small gear 1055, which is a known technique. FIG. 16 shows, by reference numeral 103A, the positions of gear teeth of the rack 103 when backlash is provided. Backlash is also inevitably present due to pitch error in the engagement of gears.
In optical disk apparatuses. the provision of such backlash is responsible for a large level of lag in a direction of the movement of the optical head 102. This lag may be several tens to several hundreds times as large as the pitch of data tracks on the optical disk. Since optical disk apparatuses need to move an optical head with considerably high precision, the removal of such backlash is required.
In the conventional technique disclosed in Japanese Patent No. 2902876, the rack 103 is pressed by the pressing spring 106 (FIG. 15A) in a direction indicated by an arrow 203 (FIG. 16) so as to remove backlash. Reference numeral 103B indicates the position of the gear teeth of the rack 103 pressed by the pressing spring 106. In this case, the gear teeth of the small gear 105S are pressed by the gear teeth of the rack 103.
Optical disk apparatuses require very highly-precise and high-speed movement of an optical head. Thus, the stability is required for the movement of an optical head. To this end, it is important to reduce a load on the movement of the optical head 102 generated between the pair of parallel guide shafts 101R and 101L and the optical head 102 as much as possible. Therefore, friction between the pair of parallel guide shafts 101R and 101L and the sliding optical head 102 needs to be reduced as much as possible.
In the above-described conventional technique, as shown in FIG. 15A, the pressing spring 106 is attached to a point 102A of the optical head 102. The pressing spring 106 is compressed so as to press the rack 103 against the small gear 105S. Therefore, a moment 204 around the guide shaft 101R is exerted on the optical head 102 by the pressing spring 106. A reaction 1901 canceling the moment 204 is generated at the guide shaft 101L, and exerted on the optical head 102. The greater the reaction 1901, the greater the friction between the guide shaft 101L and a sliding portion of the optical head 102. The large friction significantly reduces the movement stability of the optical head 102.
The number of movements of the optical head 102 may reach several millions or more before the life of the optical disk apparatuses is expired. A large number of movements of the optical head 102 lead to much abrasion of the gear teeth of the rack 103, such that the optical head 102 may be eventually brought to a state where it cannot be moved. In such a case, the rack 103 needs to be replaced. Also in the production process of optical disk apparatuses, a defective rack 103 may be found after it is already integrated into the body and therefore needs to be replaced. Therefore, it is desirable to easily replace the rack 103.
In the conventional optical disk apparatus of FIG. 15B. when the rack 103 needs to be replaced, the guide shaft 101R needs to be temporarily removed since the guide shaft 101R goes through the rack 103. When the guide shaft 101R is reattached, the tilt of the guide shaft 101R needs to be adjusted to set the tilt of the optical head 102. This adjustment typically requires considerable time and effort. As such, in the conventional technique, the rack 103 cannot be easily attached to and detached from the optical head 102.
According to one aspect of the present invention, an optical disk apparatus includes an optical head for recording data to or reproducing data from a disk having a recording region ranging from an outer circumference portion to an inner circumference portion, a first guide member having a first axis substantially parallel to the disk, for supporting the optical head in such a manner that the optical head can be moved along the first axis from an end of the outer circumference portion to an end of the inner circumference portion, a second guide member for limiting rotation of the optical head about the first axis, a rack provided on the optical head, having a reference pitch line substantially parallel to the first axis, a pinion for moving the optical head by the pinion being engaged with the rack and being rotated, and a pressing member for pressing the rack toward the pinion. The vector of a force exerted by the pinion on the rack in response to the pressing member pressing the rack toward the pinion substantially intersects the first axis.
In one embodiment of this invention, the rack is mounted on the head in such a manner that the rack can be rotated about a second axis substantially parallel to the reference pitch line.
In one embodiment of this invention, the rack is mounted on the optical head in such a manner that the rack can be attached to and detached from the optical head.
In one embodiment of this invention, a protruding portion is provided on one of the rack and the optical head, a pit portion is provided on the other of the rack and the optical head, and the rack is mounted by the optical head by engagement of the protruding portion with the pit portion.
In one embodiment of this invention, the protruding portion has a shape obtained by cutting a portion of a cylinder along a plane parallel to an axis of the cylinder, the pit portion is provided with a groove having a width smaller than a diameter of the cylinder, and the protruding portion is passed through the groove when the rack is attached to and detached from the optical head.
In one embodiment of this invention, the optical disk apparatus further includes an elastic member for pressing the rack in a direction along the second axis so as to substantially remove a gap between the rack and the optical head along the second axis.
In one embodiment of this invention, the pressing member and the elastic member are integrated together.
In one embodiment of this invention, the rack is mounted on the optical head in such a manner that a portion of the rack engaged with the pinion can be rotated about a second axis substantially parallel to the reference pitch line. The rack is made of flexible material and a portion of the rack along the second axis has a shape so that the rack can be bent about the second axis.
In one embodiment of this invention, displacement of the rack is limited to such an extent that engagement of the rack with the pinion is released when the optical head is located at a first position which is at one of the end of the inner circumference portion and the end of the outer circumference portion, and the displacement of the rack is allowed to such an extent that the engagement of the rack with the pinion is released when the optical head is located at a second position which is at the other of the end of the inner circumference portion and the end of the outer circumference portion and when a turning force greater than or equal to a predetermined value is exerted on the pinion.
In one embodiment of this invention, a first portion of the rack is engaged with the pinion when the optical head is located at the first position, and a second portion of the rack is engaged with the pinion when the optical head is located at the second position. The optical head includes a first contacting member for limiting a first contact point of the rack from being displaced away from the pinion, and a second contacting member for limiting a second contact point of the rack from being displaced away from the pinion. The first portion is located in a range between the first and second contact points of the rack. The second portion is located outside the range between the first and second contact points of the rack.
In one embodiment of this invention, the rack is mounted on the optical head in such a manner that the rack can be rotated about a second axis parallel to the reference pitch line, and the rack is deformed in such a manner that the reference pitch line and the second axis have a skewed relationship without intersection when the optical head is located at the second position and when a turning force greater than or equal to a predetermined value is exerted on the pinion.
In one embodiment of this invention, the optical disk apparatus further includes a driving section for rotating the pinion in the presence of applied driving current. The predetermined value is set so that a magnitude of the driving currents required to drive the pinion to obtain a turning force having the predetermined value, is less than or equal to a tolerable value above which a thermal influence interferes with the optical disk apparatus.
According to another aspect of the present invention, an optical disk apparatus includes an optical head for recording data to or reproducing data from a disk having a recording region ranging from an outer circumference portion to an inner circumference portion, a first guide member having a first axis substantially parallel to the disk, for supporting the optical head in such a manner that the optical head can be moved along the first axis from an end of the outer circumference portion to an end of the inner circumference portion, a second guide member for limiting rotation of the optical head about the first axis, a rack provided on the optical head, having a reference pitch line substantially parallel to the first axis, a pinion for moving the optical head by the pinion being engaged with the rack and being rotated about a third axis substantially perpendicular to the reference pitch line, and a pressing member for pressing the rack toward the pinion. A line perpendicular to both the third axis and the reference pitch line substantially intersects the first axis.
According to another aspect of the present invention, an optical disk apparatus includes an optical head for recording data to or reproducing data from a disk having a recording region ranging from an outer circumference portion to an inner circumference portion, a first guide member having a first axis substantially parallel to the disk, for supporting the optical head in such a manner that the optical head can be moved along the first axis from an end of the outer circumference portion to an end of the inner circumference portions a second guide member for limiting rotation of the optical head about the first axis, a rack provided on the optical head, having a reference pitch line substantially parallel to the first axis, a pinion for moving the optical head by the pinion being engaged with the rack and being rotated, and a pressing member for pressing the rack toward the pinion. The vector of a force exerted by the pinion on the rack in response to the pressing member pressing the rack toward the pinion substantially intersects the first axis. Displacement of the rack is limited to such an extent that engagement of the rack with the pinion is released when the optical head is located at a first position which is at one of the end of the inner circumference portion and the end of the outer circumference portion, and the displacement of the rack is allowed to such an extent that the engagement of the rack with the pinion is released when the optical head is located at a second position which is at the other of the end of the inner circumference portion and the end of the outer circumference portion and when a turning force greater than or equal to a predetermined value is exerted on the pinion.
Thus, the invention described herein makes possible the advantages of providing: (1) an optical disk apparatus capable of moving an optical head in a stable manner; and (2) an optical disk apparatus in which a rack can be easily attached to and detached from an optical head.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.